Control apparatus for electric motor of inverter system and control apparatus for electro mechanical brake

ABSTRACT

A relay switch for selectively connecting a power supply line of an inverter to a ground line is inserted between the inverter and a power source, and a power consumption unit such as a resistor element is inserted between the relay switch and ground line.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/052,742 filed Feb. 9, 2005 and claims priority of Japanese patentapplication no. 2004-054501 filed Feb. 27, 2004.

BACKGROUND OF THE INVENTION

The present invention relates to a control apparatus for an electricmotor and a control apparatus for an electro mechanical brake, and moreparticularly to a control apparatus for an electric motor of an invertersystem and a control apparatus for an electro mechanical brake to beused for a vehicle such as an automobile.

Controlling a torque of an electric motor by an inverter is applied tovarious electric motor control systems of a vehicle such as anautomobile, e.g., an electric power running system, an electric powersteering and an electro mechanical brake, respectively of an electricpower automobile.

In such electric motor control systems, a power source input to anelectric motor is short circuited in an abnormal state such as aturn-off of a main switch (e.g., refer to JP-A-9-47055).

In an electro mechanical brake using an electric motor as a thrust forcesource, as a fail safe for a defective wheel with a defect in a controlsystem including software and hardware, a fail open function has beenproposed which releases a thrust force of the defective wheel in ordernot to brake the vehicle (e.g., refer to JP-A-2002-39240 andJP-A-2003-14014). With the fail open function, when an abnormal stateoccurs, controlling an electric motor is stopped completely and a supplyof electric energy to the electric motor is stopped to thereby release athrust force.

An electro mechanical brake is installed to each of the four wheels ofan automobile. If a braking force is applied only to a particular wheelduring running, a yaw moment is applied to the vehicle about the axis ofthe braked wheel. This yaw moment curves the vehicle running directiondepending upon a vehicle running speed (vehicle speed) and a roadcondition.

SUMMARY OF THE INVENTION

An important point of whether the vehicle running direction can becontrolled to follow the handling of a driver, is a fast, instant andperfect release of an erroneous thrust force caused by a defect ormalfunction of an electric motor among others.

A short circuit connection to a ground line of a power supply line froma power source to an inverter is more effective for releasing a thrustforce, than a simple shutdown of an electric energy supply to anelectric motor by turning off a main switch.

However, each phase of an inverter is generally provided with a largecapacity smoothing condenser in order to mitigate a poor controllabilitycaused by current pulsation during a motor rotation. Therefore, even ifa power supply line to the inverter is shorted to the ground line by aswitch unit, the perfect release of a thrust force is delayed until thesmoothing condenser is completely discharged. An electro mechanicalbrake is desired to achieve the perfect release of a thrust force assoon as possible.

As described above, the issue to be solved by the present invention isto quickly extinguish the magnetization of the coil of an electric motorof an inverter control type when an abnormal state occurs and achievethe perfect release of a thrust force by an electro mechanical brake.

In order to solve the above-described issue, a control apparatus for anelectric motor to be controlled by an inverter according to the presentinvention comprises: a switching unit for selectively switching a powersupply line of the inverter to a ground line, the switching unit beinginserted between the inverter and a power source; and a powerconsumption unit inserted between the switching unit and the groundline.

In the control apparatus for an electric motor of this invention, amotor control is performed through a feedback control, and the switchingunit is closed upon occurrence of an abnormal state that a controldeviation of the feedback control takes a predetermined value or larger.

In the control apparatus for an electric motor of this invention, theinverter is of a microcomputer control type, two microcomputers executea same calculation process, and if calculation results by twomicrocomputers are not coincident, the switching unit is closed.

In the control apparatus for an electric motor of this invention, theelectric motor is a drive source for an electro mechanical brake.

A control apparatus for an electro mechanical brake for generating athrust force by making an electric motor to be controlled by an inverterpush brake pads against a brake disk, according to the present inventioncomprises: a switching unit for selectively switching a power supplyline of the inverter to a ground line, the switching unit being insertedbetween the inverter and a power source; and a power consumption unitinserted between the switching unit and the ground line.

The control apparatus for an electro mechanical brake of this inventionfurther comprises a thrust force detecting unit for detecting a thrustforce applied to the brake pads, wherein a feedback control is performedfor the thrust force detected with the thrust force detecting unit, andthe switching unit is closed upon occurrence of an abnormal state that acontrol deviation of the feedback control takes a predetermined value orlarger.

In the control apparatus for an electro mechanical brake of thisinvention, the inverter is of a microcomputer control type, twomicrocomputers execute a same calculation process, and if calculationresults by two microcomputers are not coincident, the switching unit isclosed.

According to the control apparatus of this invention, for the electricmotor, when an abnormal state occurs, the switching unit insertedbetween the inverter and power source connects the power source line ofthe inverter to the ground line and a power is consumed by the powerconsumption unit via the ground line. Discharge of smoothing condensersof the inverter can be performed at high speed, and coil magnetizationof the electric motor can be distinguished at once. For the electromagnetic brake, a thrust force can be released completely and quickly.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a control apparatus for an electromechanical brake adopting a control apparatus for an electric motoraccording to a first embodiment of the present invention.

FIGS. 2A to 2C are timing charts illustrating the operation of the firstembodiment.

FIG. 3 is a circuit diagram of a control apparatus for an electromechanical brake adopting a control apparatus for an electric motoraccording to a second embodiment of the present invention.

FIG. 4 is a flow chart illustrating a control sequence of the secondembodiment.

FIG. 5 is a circuit diagram of a control apparatus for an electromechanical brake adopting a control apparatus for an electric motoraccording to a third embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

With reference to the accompanying drawings, detail description will bemade on embodiments of a control apparatus for an electric motor and acontrol apparatus for an electro mechanical brake according to theinvention.

FIG. 1 shows the first embodiment of an electro mechanical brake. Theelectro mechanical brake 10 is mounted on each vehicle wheel and has abrake disk rotor 11 and an electric power caliper 12.

The electric power caliper 12 has a pair of brake pads 13 and 14 mountedon both sides of the brake disk rotor 11 and an electric motor 15 as abraking force generator for driving the brake pads 13 and 14. Theelectric power caliper 12 brakes the wheel by squeezing the brake diskrotor 11 between the brake pads 13 and 14.

As the electric motor 15, a three-phase electric motor (three-phase a.c.electric motor) is generally used because of the structural advantagesin terms of controllability and lifetime.

The electric power caliper 12 has a built-in structure for converting arotation motion of the electric motor 15 by coil magnetization into alinear motion. The electric power caliper 12 is a device for linearlymoving the brake pads 13 and 14 to squeeze (push) the brake disk rotor11 and generate a thrust force, and while the electric motor 15 is notunder coil magnetization, the brake pads 13 and 14 are moved away fromthe brake disk rotor 11 by using built-in springs (not shown).

The electric power caliper 12 has a thrust force sensor 16 for sensing agenerated thrust force. The electric motor 15 has a rotation positionsensor 17 for detecting a motor rotation position and a current sensor18 for detecting a motor drive current.

An electric power of a battery power source (d.c. power source) 21 isconverted by an inverter 31 and supplied to the electric motor 15.

The inverter 31 has three-phase bridge drive elements 32, 33, 34, 35, 36and 37 and smoothing condensers 38, 39 and 40. The inventer 31 is of aPWM type, i.e., a pulse width modulation type. A three-phase driver IC41 switches the three-phase bridge drive elements 32, 33, 34, 35, 36 and37 at timings determined by a duty signal of a PWM output from amicrocomputer 42, to thereby control the rotation direction and rotationspeed (rotation number) of the electric motor 15.

The smoothing condensers 38, 39 and 40 or capacitors provided torespective phases of the inverter 31 mitigate a poor controllability dueto current pulsation during motor rotation.

The microcomputer 42 has as its inputs: an operation signal Sbcorresponding to a depression amount of a not-shown brake pedal; asignal representative of an actual thrust force Tb output from thethrust force sensor 16; a signal representative of the motor rotationposition output from the rotation position sensor 17; and a signalrepresentative of a motor drive current output from the current sensor18, generates a thrust force command value Ta through calculation of afeedback control of a thrust force, and outputs a duty signal for PWMcontrol corresponding to the thrust force command value Ta to thethree-phase driver IC 41.

A relay switch 43 as a switch unit is disposed between the battery powersource 21 and inverter 31.

The relay switch 43 has: an inverter side contact 43A connected to apower supply line 31 vb of the inverter 31; a battery side (power supplyside) contact 43B connected to the anode side of the battery powersource 21; and a ground side contact 43C connected to a ground line GND.The relay switch 43 is switched in response to an output signal from anarithmetic comparison unit 45. In a normal state, the inverter sidecontact 43A is connected to the battery side contact 43B, and in anabnormal state, the inverter side contact 43A is connected to the groundside contact 43C.

The ground side contact 43C is connected to the ground line via a powerconsumption resistor element 44.

In this embodiment, the arithmetic comparison unit 45 is a comparatormade of an OP amplifier or the like. The arithmetic comparison unit 45has as its inputs the thrust force command value Ta computed by themicrocomputer 42 and the actual thrust force Tb output from the thrustforce sensor 16, and compares the thrust force command value Ta andactual thrust force Tb. If a deviation F=the actual thrust force Tb−thethrust force command value Ta is equal to or smaller than a thresholdvalue Fth, the arithmetic comparison unit 45 connects the inverter sidecontact 43A of the relay switch 43 to the battery side contact 43B. Ifonly the state that the deviation F is larger than the threshold valueFth continues for a set time tth or longer, this state is judgedabnormal, and the arithmetic comparison unit 45 outputs a signal (Hlevel signal and L level signal) to connect the inverter side contact43A to the ground side contact 43C.

With reference to FIGS. 2A to 2C, description will be made on anoperation to be executed when an abnormal state occurs in the electromechanical brake system and an abnormal thrust force not intended isgenerated by the electric power caliper 12.

In FIGS. 2A to 2C, reference symbol Ta represents the thrust forcecommand value computed by the microcomputer 42, and reference symbol Tbrepresents the actual thrust force generated by the electric powercaliper 12.

In the normal state, the actual thrust force Tb is generated whichfollows the thrust force command value Ta under the thrust force controlby the microcomputer 42.

In some cases, a thrust force control deviation Fx or a response delaytx relative to the thrust force command value Ta may occur because ofthe influence of inertia of structural components of the electric powercaliper. However, unless the state that the control deviation is largerthan the value Fth continues for the set time tth or longer, the stateis not judged abnormal and the ordinary thrust force control by themicrocomputer 42 continues.

If any abnormal state occurs in the electro mechanical brake system andthe state that the control deviation is larger than the value Fthcontinues for the set time tth or longer, it is judged that anabnormally excessive thrust force is apparently applied to the electromechanical brake 10 of the wheel.

As an abnormal thrust force is applied only to a particular wheel, a yawmoment is applied to the vehicle, resulting in a running directiondifferent from the steering by the driver.

A signal representative of the actual trust force Tb and the thrustforce command value Ta are input to the arithmetic comparison unit 45which always compare the actual thrust force Tb with the thrust forcecommand value Ta.

When the abnormal thrust force is generated, at the time Toff, theoutput signal of the arithmetic comparator unit 45 transits from apreset H level signal (normal) to an L level signal (abnormal) so thatthe inverter side contact 43A of the relay switch 43 is switched fromthe battery side contact 43B to the ground side contact 43C.

The power supply (supply of a battery voltage VB) to the inverter 31 istherefore turned off. The power supply line 31 vb of the inverter 31 isconnected via a power consumption unit 44 to the ground line GND to forma closed circuit on the inverter side.

With this closed circuit, the power accumulated in the smoothingcondensers 38, 39 and 40 of the inverter 31 is consumed in the powerconsumption unit 44 and the power source side voltage of the inverter 31lowers to the zero level quickly after the time Toff. Discharge of thesmoothing condensers 38, 39 and 40 is executed at high speed and thecoil magnetization of the electric motor 15 extinguishes quickly.

Even if the three-phase driver IC 41 executes the rotation control, thecoil magnetization of the electric motor 15 is extinguished at once. Asthe coil magnetization is extinguished at once, the thrust forcegenerated by the electric power caliper 12 is completely released atonce so that the vehicle running direction caused by the abnormal thrustforce and not intended can be avoided.

When an abnormal thrust force is generated, without involving the relayswitch 43 and power consumption unit 44, the control by themicrocomputer 42 may be stopped or the gates of the drive elements 32 to37 for the inventer 31 may be turned off, to thereby stop the powersupply to the electric motor. However, in this case, the coilmagnetization of the electric motor 15 cannot be extinguished at oncebecause of a time delay to be caused by a computation time of themicrocomputer 42, the accumulated power in the smoothing condensers 38to 40, a turn-off time of the drive elements 32 to 37 and the like.

If an abnormal thrust force is generated by a failure of themicrocomputer 42 and a defective open/short of the drive elements 32 to37 and the like, it is not effective to stop the control by themicrocomputer 42 or turn off the gates of the drive elements 32 to 37 ofthe inverter 31 to stop the supply of a power to the electric motor 15.

In this embodiment, the electric power source is basically shut down byusing the relay switch 43 and the electric energy remaining in thesystem electric series is consumed quickly by the power consumption unit44 so that the coil magnetization of the electric motor 15 can beextinguished quickly.

With reference to FIG. 3, description will be made on the secondembodiment in which the control apparatus for the electric motor of thepresent invention is applied to the control apparatus for an electromechanical brake. In FIG. 3, components similar to those shown in FIG. 1are represented by identical reference numerals to those shown in FIG. 1and the description thereof is omitted.

In the second embodiment, the arithmetic comparison for generating acommand signal to the relay switch 43 is performed by software of themicrocomputer 42, i.e., by a program to be executed by the microcomputer42.

An arithmetic comparison routine 46 is executed by a real timeinterrupt. The microcomputer 42 compares the signal representative ofthe thrust force Tb input from the thrust force sensor 16 with thethrust force command value Ta obtained by the arithmetic process by themicrocomputer 42. If a deviation F=the actual thrust force Tb−the thrustforce command value Ta is equal to or smaller than a threshold valueFth, the inverter side contact 43A of the relay switch 43 is connectedto the battery side contact 43B. If only the state that the deviation Fis larger than the threshold value Fth continues for a set time tth orlonger, this state is judged abnormal, and a signal (H level signal andL level signal) is output to connect the inverter side contact 43A tothe ground side contact 43C.

With reference to the flow chart shown in FIG. 4, a specific processsequence of the arithmetic comparison routine 46 will be described.

First, the value written in F_for_CONT as the actual thrust force value(Tb), F_for_CONT being a RAM in the microcomputer 42, is compared with apredetermined thrust force limit value F_LIMT (Step 51). Since the limitvalue F_LIMT changes with the thrust force command value Ta, it isobtained by multiplying a predetermined coefficient or the valueextracted from a map or the like is used.

In the comparison process at Step 51, if the value written in F_for_CONTis in excess of the thrust force limit value F_LIMT, a variable CNT forcounting a thrust force abnormal state is incremented (Step 52).

On the other hand, if the value written in F_for CONT is not in excessof the thrust force limit value F_LIMT, the variable CNT is cleared to 0(Step 53).

If the variable CNT is incremented, the value of the variable CNT iscompared with an abnormal state limit counter value LIMT_CNT which is apredetermined constant (Step 54). If the value of the variable CNT is inexcess of the limit counter value LIMT_CNT, a process R_RLY=OFF isexecuted which switches the relay switch 43 (Step 55). The inverter sidecontact 43A of the relay switch 43 is therefore switched from thebattery side contact 43B to the ground side contact 43C.

Similar to the first embodiment, with this switching, the power supply(supply of the battery voltage VB) to the inverter 31 is thereforeturned off. The power supply line 31 vb of the inverter 31 is connectedvia the power consumption unit 44 to the ground line GND to form aclosed circuit on the inverter 31 side. With this closed circuit, thepower accumulated in the smoothing condensers 38, 39 and 40 of theinverter 31 is consumed in the power consumption unit 44 and the powersource side voltage of the inverter 31 lowers to the zero level quicklyafter the time Toff.

Even if the three-phase driver IC 41 executes the rotation control, thecoil magnetization of the electric motor 15 is extinguished at once. Asthe coil magnetization is extinguished at once, the thrust forcegenerated by the electric power caliper 12 is completely released atonce so that the vehicle running direction caused by the abnormal thrustforce and not intended can be avoided.

According to the second embodiment, the arithmetic comparison unit 45 ofthe first embodiment can be omitted and the structure can be simplified.There is therefore the merit that the parameter for extinguishing thethrust force can be changed freely.

With reference to FIG. 5, description will be made on the thirdembodiment in which the control apparatus for the electric motor of thepresent invention is applied to the control apparatus for an electromechanical brake. Also in FIG. 5, components similar to those shown inFIG. 1 are represented by identical reference numerals to those shown inFIG. 1 and the description thereof is omitted.

The third embodiment has a second microcomputer 47 in addition to themicrocomputer 42 (in this embodiment, hereinafter called a firstmicrocomputer 42). The first and second microcomputers 42 and 47 cancommunicate with each other.

Similar to the first embodiment, the first microcomputer 42 has as itsinputs: an operation signal corresponding to a depression amount of anunrepresented brake pedal; a signal representative of the actual thrustforce Tb output from the thrust force sensor 16; a signal representativeof the motor rotation position output from the rotation position sensor17; and a signal representative of a motor drive current output from thecurrent sensor 18, generates the thrust force command value Ta throughcalculation of the input signals, and outputs a duty signal for PWMcontrol corresponding to the thrust force command value Ta to thethree-phase driver IC 41.

The second microcomputer 47 requests the first microcomputer 42 for thecalculation, and compares the calculation result by the firstmicrocomputer 42 with the calculation result by the second microcomputer47 to thereby judge whether the calculation function of the firstmicrocomputer 42 is normal.

Namely, the first and second microcomputers 42 and 47 execute the samecalculation process and if the calculation results by the microcomputers42 and 47 are not coincident, it is judged abnormal.

In accordance with this judgement result, the second microcomputer 47outputs a signal (H level signal and L level signal) to a NAND gate 48.If the calculation result is not abnormal, the second microcomputer 47outputs the H level signal to the NAND gate 48, whereas if thecalculation result is abnormal, the second microcomputer 47 outputs theL level signal to the NAND gate 48.

The NAND gate 48 receives the signal from the second microcomputer 47 aswell as the relay switch control signal (H level signal and L levelsignal) equivalent to the signal output from the arithmetic comparisonunit 45 of the first embodiment, and outputs a signal representative ofa NAND logical value to the relay switch 43.

With this structure, even if any one of the first and secondmicrocomputers 42 and 47 and arithmetic comparison unit 45 becomesdefective, it is possible to switch the inverter side contact 43A of therelay switch 43 to the ground side contact 43C when an abnormal thrustforce is generated.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A control apparatus for an electric motor to be controlled by aninverter, comprising: switching means for selectively switching a powersupply line of said inverter to a ground line, said switching meansbeing inserted between said inverter and a power source; and powerconsumption means inserted between said switching means and said groundline.
 2. The control apparatus for an electric motor according to claim1, wherein a motor control is performed through a feedback control, andsaid switching means is closed upon occurrence of an abnormal state thata control deviation of the feedback control takes a predetermined valueor larger.
 3. The control apparatus for an electric motor according toclaim 1, wherein said inverter is of a microcomputer control type, twomicrocomputers execute a same calculation process, and if calculationresults by two microcomputers are not coincident, said switching meansis closed.
 4. The control apparatus for an electric motor according toclaim 2, wherein said inverter is of a microcomputer control type, twomicrocomputers execute a same calculation process, and if calculationresults by two microcomputers are not coincident, said switching meansis closed.
 5. The control apparatus for an electric motor according toclaim 1, wherein said electric motor is a drive source for an electromechanical brake.
 6. The control apparatus for an electric motoraccording to claim 2, wherein said electric motor is a drive source foran electro mechanical brake.
 7. The control apparatus for an electricmotor according to claim 3, wherein said electric motor is a drivesource for an electro mechanical brake.
 8. A control apparatus for anelectro mechanical brake for generating a thrust force by making anelectric motor to be controlled by an inverter push brake pads against abrake disk, comprising: switching means for selectively switching apower supply line of said inverter to a ground line, said switchingmeans being inserted between said inverter and a power source; and powerconsumption means inserted between said switching means and said groundline.
 9. The control apparatus for an electro mechanical brake accordingto claim 8, further comprising thrust force detecting means fordetecting a thrust force applied to said brake pads, wherein a feedbackcontrol is performed for the thrust force detected with said thrustforce detecting means, and said switching means is closed uponoccurrence of an abnormal state that a control deviation of the feedbackcontrol takes a predetermined value or larger.
 10. The control apparatusfor an electro mechanical brake according to claim 8, wherein saidinverter is of a microcomputer control type, two microcomputers executea same calculation process, and if calculation results by twomicrocomputers are not coincident, said switching means is closed. 11.The control apparatus for an electro mechanical brake according to claim9, wherein said inverter is of a microcomputer control type, twomicrocomputers execute a same calculation process, and if calculationresults by two microcomputers are not coincident, said switching meansis closed.